U.S. patent number 6,148,200 [Application Number 09/091,950] was granted by the patent office on 2000-11-14 for load reduction of a visitor location register.
This patent grant is currently assigned to Nokia Telecommunications Oy. Invention is credited to Lauri Lahtinen.
United States Patent |
6,148,200 |
Lahtinen |
November 14, 2000 |
Load reduction of a visitor location register
Abstract
A problem arises when the data of the visitor location register
(VLR) are lost for some reason. In this case, only the visitor
location register (VLRn) in whose area the mobile station (MS) is
located is known. The mobile station (MS) must then be paged in all
location areas (LAn) of the visitor location register (VLR). Such
paging of mobile stations causes a significant overload. The
overload is reduced, according to the invention, by dividing the
area covered by a physical visitor location area (VLR) into areas
of a plurality of logical visitor location registers (LVLRn). In
connection with location updatings, not only the physical visitor
location register (VLR) is stored by also information on the
logical visitor location register (LVLRn) in whose area the mobile
station (MS) is located; in a problematic situation where the
switching centre (MSC) is not aware of the location area of the
mobile station(MS), the mobile station (MS) is paged, at least at
first, only in the area of the logical visitor location register
(LVLRn).
Inventors: |
Lahtinen; Lauri (Espoo,
FI) |
Assignee: |
Nokia Telecommunications Oy
(Espoo, FI)
|
Family
ID: |
8544632 |
Appl.
No.: |
09/091,950 |
Filed: |
June 26, 1998 |
PCT
Filed: |
December 20, 1996 |
PCT No.: |
PCT/FI96/00685 |
371
Date: |
June 26, 1998 |
102(e)
Date: |
June 26, 1998 |
PCT
Pub. No.: |
WO97/24898 |
PCT
Pub. Date: |
July 10, 1997 |
Foreign Application Priority Data
Current U.S.
Class: |
455/433; 455/446;
455/449; 455/458 |
Current CPC
Class: |
H04W
68/00 (20130101) |
Current International
Class: |
H04Q
7/38 (20060101); H04Q 007/20 () |
Field of
Search: |
;455/422,433,435,443,444,445,446,448,449,458,560,456 |
Foreign Patent Documents
|
|
|
|
|
|
|
0 475 865 |
|
Mar 1992 |
|
EP |
|
0 666 700 |
|
Aug 1995 |
|
EP |
|
WO 92/13428 |
|
Aug 1992 |
|
WO |
|
WO 96/07277 |
|
Mar 1996 |
|
WO |
|
Primary Examiner: Trost; William G.
Assistant Examiner: Persino; Raymond B.
Attorney, Agent or Firm: Altera Law Group, LLC
Claims
What is claimed is:
1. A method for updating location of a mobile station (MS) in a
digital mobile telephone network (NSS), wherein one home location
register (HLR) stores information on the physical visitor location
register (VLR) in the area of which the mobile station (MS) is
located, characterized in that
the area covered by a physical visitor location register (VLR) is
divided into areas of a plurality of logical visitor location
registers (LVLRn); and
the home location register (HLR) stores, in addition to the
physical visitor location register (VLR), information on the
logical visitor location register (LVLRn) in whose area the mobile
station (MS) is located.
2. A method according to claim 1 characterized in that said
physical visitor location register (VLR) is divided hierarchically,
whereby each logical visitor location register (LVLR) is subject to
a single physical visitor location register (VLR).
3. A method according to claim 2, characterized in that said areas
of said logical visitor location registers (LVLRn) are formed on
the basis of geographical location, each area preferable comprising
a small integer number of location areas.
4. A method according to claim 1, characterized in that said areas
of said logical visitor location registers (LVLRn) are formed on
the basis of geographical location, each area preferably comprising
a small integer number of location areas.
5. A method for paging a mobile station (MS) in the area of a
mobile services switching centre (MSC) in a digital mobile
telephone network wherein, at any time, the location area (LA) of a
mobile station (MS) is maintained in one Visitor Location Register
(VLR) and the information on the VLR is maintained in one Home
Location Register (HLR), when information on the location area (LA)
of the mobile station (MS) has been lost by the switching centre
(MSC), characterized in that
the area covered by the physical visitor location register (VLR) of
the switching centre (MSC) is divided into areas of a plurality of
logical visitor location registers (LVLRn); and
the mobile station (MS) is paged, at least at first, only in the
area of the logical visitor location register (LVLRn) last
indicated by the mobile station.
6. A method according to claim 5, characterized in that said
physical visitor location register (VLR) is divided hierarchically,
whereby each logical visitor location register (LVLR) is subject to
a single physical visitor location register (VLR).
7. A method according to claim 6, characterized in that said areas
of said logical visitor location registers (LVLRn) are formed on
the basis of geographical location, each area preferable comprising
a small integer number of location areas.
8. A method according to claim 5, characterized in that said areas
of said logical visitor location registers (LVLRn) are formed on
the basis of geographical location, each area preferable comprising
a small integer number of location areas.
9. A mobile services switching centre (MSC) in a digital mobile
telephone network wherein, at any time, the location information of
a mobile station (MS) is maintained in one Visitor Location
Register (VLR) and the information on the VLR is maintained in one
Home Location Register (HLR), said mobile services switching centre
(MSC) comprising a physical visitor location register (VLR) and
being adapted to transmit information to a home location register
(HLR) of the mobile telephone network on the physical visitor
location registers (VLR) in the area of which each mobile station
(MS) is located, characterized in that
the area covered by the physical visitor location register (VLR) of
the switching centre (MSC) is divided into areas of a plurality of
logical visitor location registers (LVLRn); and
the switching centre (MSC) is also adapted to transmit information
to the home location register (HLR) on the logical visitor location
registers (LVLRn) in the area of which each mobile station (MS) is
located.
10. A location update message in a digital mobile telephone network
(NSS) wherein, at any time, the location information of a mobile
station (MS) is maintained in one Visitor Location Register (VLR)
and the information on the VLR is maintained in one Home Location
Register (HLR), said location update message containing information
on the visitor location register (VLR) in whose area the mobile
station (MS) is located, characterized in that the location update
message further contains information on the logical visitor
location register (LVLRn) in the area of which the mobile station
(MS) is located.
Description
The invention relates to mobile communication systems and
particularly to reducing the load of their visitor location
registers.
FIG. 1 illustrates the roaming of a mobile station MS in a mobile
communication network or in a network subsystem NSS. In this
example, the NSS comprises six base transceiver stations BTS1 to
BTS6, which can be controlled by one or more base station
controllers BSC. Each base station BTS serves one cell. When an MS
terminated call is switched through the network NSS, the NSS must
know the area in which the MS is to be paged. The area in which the
MS is paged is called a location area LA.
The size of the location area LA is a compromise. If the location
area is very large, the MS must be paged in the area of several
base stations BTS. This means that mobile stations are also paged
in base station areas where they are not located. This consumes the
capacity of radio channels. If the location area is small, location
updatings must be performed frequently. FIG. 1 shows, by way of
illustration, three location areas LA1-LA3, which cover 1, 2 and 3
base stations, respectively. The base stations BTS continuously
broadcast information on themselves and their environment, such as
a base station identifier BSI and a location area identifier LAI.
On the basis of the LAI, an MS registered in a BTS knows in which
LA it is located at each moment. If the MS, when changing the BTS,
observes that the LAI has changed, it sends a location update
request or message to the network NSS. The LA of the MS is updated
in the visitor location register VLR in whose area the MS is
located at that moment. The VLR typically stores e.g. the
subscriber's IMSI (International Mobile Subscriber Identity)
number, MSISDN number, subscriber service data and LAI.
Information on the VLR in whose area the MS is located is sent to
the home location register of the MS. The HLR stores permanent
subscriber data, which are not dependent on the subscriber's
location at a given moment: e.g. the subscriber's MSISDN and IMSI,
subscriber service data, and routing data to the VLR in whose
location area the MS is located.
FIG. 2 illustrates the setting up of an MS terminated call in a
GSM-type mobile communication system. If the MS of FIG. 1 is not
located within the area of its own home location register, the
parts of FIG. 2 correspond to those of FIG. 1; however, the HLR and
VLR are associated with different mobile services switching centres
MSC. In step 1, a call arrives at a gateway mobile switching centre
GMSC. In step 2, the GMSC defines the subscriber's home location
register HLR on the basis of the called subscriber's directory
number MSISDN, and sends it a request for routing data. Information
on the VLR in whose area the subscriber is located is updated in
the subscriber's HLR in connection with location updating. On the
basis of this information, the HLR sends the VLR a `Provide Roaming
Number` request in step 3. The IMSI of the MS subscriber is also
sent to the VLR in this request. In step 4, the VLR stores the data
it has received and assigns a mobile station roaming number MSRN.
In step 5, the VLR sends the MSRN it has assigned to the HLR, which
in step 6 sends it to the switching centre GMSC that requested the
routing data. The roaming number domain is defined in such a way
that a call is always directed to the MSC whose VLR has assigned
the roaming number in question. On the basis of the MSRN, the GMSC
is thus able to route the call forward by sending an initial
address message in step 7 to the MSC indicated by the MSRN.
In this example, the MSC finds out on the basis of the MSRN that
the call will terminate in its own area. In step 8, the MSC
requests the data of the called subscriber from its own VLR call
set-up. In a normal case, the VLR returns the requested data in
step 9 for setting up the call. This is indicated by arrows 10 and
11.
A problem arises when the data of the VLR are lost for some reason.
This may happen, for instance, when the VLR is reinitialized,
possibly during software updating or equipment maintenance. In this
case, only the VLR in whose area the MS is located is known (on the
basis of the HLR of the MS). The MS must then be paged in all
location areas LA where there are mobile stations whose data are
stored in the VLR in question. If the VLR serves a large number of
subscribers, such paging of mobile stations causes a significant
overload mainly in three areas: 1) between the MSC and the base
station system BSS; 2) in the signalling process of the BSS; and 3)
on radio channels. The BSS comprises a base station controller BSC
and base stations BTS controlled by the BSC. As a result of the
overload, some of the MS terminated calls fail.
The object of the invention is thus to provide a method and an
apparatus implementing the method in such a manner that the
above-mentioned overload problems are solved. The objects of the
invention are achieved with methods and systems characterized by
what is disclosed in the independent claims. Preferred embodiments
are disclosed in the dependent claims.
The invention is based on dividing the area of a physical VLR into
areas of a plurality of logical VLRs. When a mobile station
performs location updating, the location update request sent by the
VLR to the HLR also contains information on the logical VLR in
whose area the mobile station is located. This information is
transparent to the HLR, i.e. the HLR stores it but does not react
to it in any way.
In the case of an incoming call, signalling takes place as before.
In a problematic situation where the VLR is not aware of the
location area of the MS, the physical VLR receives the address of
the logical VLR of the MS from the HLR with normal signalling. This
information is included in a `Provide Roaming Number` message. The
physical VLR thus limits the paging to the area of the logical VLR.
In the most extreme case, the area of the logical VLR may even be
only one location area.
It is an advantage of the method and system of the invention that
the network is considerably less loaded in problematic situations
than in prior art systems. Another advantage of the arrangement of
the invention is that the modifications to be made in an existing
system are relatively small, for instance modifications in the MSC
software. The modifications are compatible with the existing
systems in every respect. A network can thus employ--simultaneously
and in a flexible manner--both switching centres modified according
to the invention and switching centres not modified according to
the invention.
In the following, the invention will be described in greater detail
by means of preferred embodiments with reference to the
accompanying drawings, in which
FIG. 1 shows the parts of a mobile telephone network that are
essential to the invention;
FIG. 2 shows the steps of a signalling process of a mobile
telephone network that are essential to the invention; and
FIG. 3 shows location areas of a mobile telephone network, divided
into areas of a plurality of logical visitor location
registers.
With reference to FIG. 3, the overload of a mobile telephone
network is limited, according to the invention, by dividing the
area of a physical visitor location register VLR into areas of a
plurality of logical visitor location registers LVLRn. For reasons
of clarity, the area of the physical VLR is divided in FIG. 3 into
areas of only two logical visitor location registers LVLR1 and
LVLR2. In practical applications, a suitable number n of LVLRs in
the area of one physical VLR could be, for example, 5 to 10. The
system of FIG. 3 would require the following modifications in the
prior art solution of FIGS. 1 and 2:
1. Defining and naming LVLRs of suitable size. In the naming, it is
sufficient to use, for example, 1 or 2 digits after the number of
the VLR.
2. The message sent by the MSC to the HLR in connection with the
location updating of an MS also contains information on the LVLR in
whose area the MS is located. This information is transparent to
the HLR, i.e. the HLR processes it as an ordinary number of a
physical VLR which is only 1 or 2 digits longer than it would be
without the identifier n of the LVLR.
3. In the case of an MS terminated call, the changes will not
become visible until the data of the VLR have been lost for one
reason or another, i.e. the VLR does not know the location area of
the MS. In this case, the MSC (and its VLR) receives the identifier
of the LVLR of the MS from the HLR in connection with normal
signalling (in a `Provide Roaming Number` message). On the basis of
this information, the MSC may limit the paging of the MS to only
the area of the LVLR.
According to the prior art, the following information, for example,
is stored in a HLR:
______________________________________ an MS whose IMSI number is
in the area of a VLR is whose GT address is IMSI NCC NDC VLRn
______________________________________
where:
GT=Global Title
NCC=National Country Code
NDC=National Destination Code
VLRn=Visitor Location Register number.
According to the invention, the following information is
correspondingly stored in the HLR:
______________________________________ an MS whose IMSI number is
in the area of a VLR is whose GT address is IMSI NCC NDC VLRn nn
______________________________________
where
nn=the number of the LVLR (1 or 2 digits) within the physical
VLRn.
The specification of a VLR as LVRLs is implemented according to the
invention for instance as software modifications in the MSC. The
software modifications are as follows:
1. The MSC must keep a log of which location areas LAn belong to
which logical visitor location registers LVLRn.
2. In connection with location updating of an MS, the MSC must also
send the HLR of the MS information on the LVLRn in whose area the
MS is located.
3. In problematic situations where the data of the physical VLR
have been lost, the MSC must, when paging the MS, at least at first
limit the paging to only the LVLRn area where the location of the
MS has last been updated.
Dividing a visitor location register VLR into (or specifying a VLR
as) logical visitor location registers LVLRn reduces the congestion
peaks occurring in problematic situations. If the number n of LVLRs
within the area of a physical VLR is five, for example, the MS must
be paged in an area that is five times smaller, and the load caused
by the paging is reduced accordingly. There is, nevertheless, a
side effect: the number of location updatings grows by the same
coefficient. However, the advantages resulting from the reduction
of congestion peaks outnumber the drawbacks caused by the
additional traffic caused the location updatings.
It will be obvious to one skilled in the art that the examples
described above are in every respect intended to illustrate the
invention, not to restrict it. The invention has been described, by
way of example, with reference to a GSM system, but it may also be
applied to other kinds of mobile communication systems. The
invention and its embodiments are thus not limited to the examples
described above, but they may be modified within the scope of the
appended claims.
* * * * *